Biomarkers of specific targets are becoming an essential objective for clinical unmet clinical needs to improve diseases early detection and increase patient overall survival. Ovarian cancer is among the highest mortality gynecological cancers. It is asymptomatic and almost always diagnosed at advanced stage. At five years from the first diagnosis the survival rate of ovarian cancer patients is only 30%. Cyclooxygenase (COX)-1 as opposed to COX-2 is known to be overexpressed in ovarian cancer. Therefore, fluorescent probes targeting COX-1 were designed and prepared in fair to good yields for its quantitatively detection in human ovarian cancer cell lines (OVCAR-3 and SKOV-3). In particular, both cytofluorimetric and immunofluorescent experiments showed that N-[4-(9-dimethylimino-9H-benzo[a]phenoxazin-5-ylamino)butyl]-2-(3,4-bis(4-methoxyphenyl)isoxazol-5-yl)acetamide chloride (11) enters into OVCAR-3 cells and is mainly localized on the membrane containing the COX-1. Membrane fluorescence emission represents about 80% of the total fluorescence measured in the whole cell, while the non-specific labeling represents only 20%. This result indicates that the intensity of fluorescence emission is almost exclusively attributable to 11 bound to COX-1 located on the membrane. Furthermore, no diffusion inside the cell occurs. IC50 hCOX-1 value of 11 determined by measuring the O2 consumption during the bis-oxygenation of the arachidonic acid catalysed by COX-1 was found to be equal to 1.8 nM. Furthermore, 11 inhibits oCOX-1 with IC50 = 6.85 nM and mCOX-2 with IC50 = 269.5 nM; the corresponding selectivity index SI is equal to 39.3 against oCOX-1. 11 inhibits oCOX-1 at 0 min of incubation with 91% inhibition, whereas in the same time it does not inhibit mCOX-2. Fingerprints for Ligands and Proteins (FLAP) software calculations were performed to justify 11 higher COX-1 inhibitory potency than mofezolac (COX-1 IC50 = 5.1 nM), which in turn is a moiety of 11. Specifically, the two compounds bind differently in the COX-1 active site.
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